When Does Life Begin? | Scientifically

| Conception’s Significance |

  1. Is an Embryo a Baby? | Scientifically
  2. Is an Embryo a Baby? | Biblically

A Good Question

As I’ve done elsewhere, let me start by saying that this is a good question. It’s a question that most of us have wondered at some point and one that we all need an answer to. Our answer to this question not only informs our perspective on current issues, but it defines the foundation for so many decisions we’ll make regarding starting and planning our families. It’s important we not only have an answer to this question, but we have a certainty about why this is the answer.

Before we begin, I want to let you know that I plan to discuss this question objectively here. Please don’t let my objectivity imply that I don’t care about what this question means to all of us.  I know how emotional this question can be, especially for those who have had a miscarriage, done IVF, or have found themselves ending a pregnancy. We share some of our heart for those situations on different parts of our website, such as our post for Mother’s Day, but if you’ll allow me, I’d like to the focus of this page solely on finding the answer to this question objectively.

A Scientific Approach

On this page, as we answer the question of When Does Life Begin, we will strictly look through the lens of science. For those who share our faith, this simply means that God has made the truth about when life begins evident in His creation. So, as we study the order in His creation, we can learn the answer to this question. Hopefully this approach might even help to answer this question for those who don’t share our faith or just aren’t sure about all that yet.

To do this, let’s turn to the science of biology which is the study of (“-ology”) life (“bio-”). The question we would ask biology is “When is something alive?” In order to answer this question, biologists identified the characteristics that are common to all living things.  According to biology, something is alive if it possesses all these characteristics.  These characteristics have been described with a variety of detail (e.g. some textbooks break them into five and others into eight), but for our purposes here we will use the most authoritative source for defining these characteristics, a textbook. Specifically, the Prentice Hall Biology textbook states this: “living things share the following characteristics:

  • Living things are made up of units called cells.
  • Living things reproduce.
  • Living things are based on a universal genetic code.
  • Living things grow and develop.
  • Living things obtain and use materials and energy.
  • Living things respond to their environment.
  • Living things maintain a stable internal environment.
  • Taken as a group, living things change over time.”[1]

It might be helpful to note that virtually all biologists would readily agree that the first cell formed at conception (zygote) is a living organism.  The disparity in scientific opinion regards when this living thing is a person (i.e. has a soul). For that discussion, see our page on When is a Person a Person | Scientifically. Our scope here is simply to confirm and more clearly outline what is already commonly accepted: that the first cell formed during fertilization (conception) is indeed a living organism.

Depending on your current opinion, the terminology I use to describe this living organism (i.e. “it” or “baby”) could be offensive. I’d prefer to remove this stumbling block, so let me borrow from Merriam Webster’s definition of an embryo for now: “developing human individual”. In order to determine when life begins, let’s explore each of these characteristics of life in sequence to determine if and when each is present for the developing human individual.

Made up of Cells

Our textbook explains that “living things, or organisms, are made up of small, self-contained units called cells. A cell is a collection of living matter enclosed by a barrier that separates the cell from its surroundings. Cells are the smallest units of an organism that can be considered alive.”[1] So, at what point is the developing human individual made up of cells?

Before we go any farther, it would be helpful to take a step back and briefly describe the process of fertilization (conception).  Leading up to fertilization, hundreds of millions of sperm are released by the man into the woman to race to fertilize a single egg (ovum) released by the woman.  At the moment of conception, one of these sperm cells will join with the single egg cell released by the woman.  This begins the process of fertilization wherein the DNA from the sperm cell combines with the DNA from the egg cell to form the first cell (zygote) of the developing human individual.  This cell then begins to divide and develop as it travels down the fallopian tube toward the uterus (womb) where implantation will occur.

To be more specific to our question, immediately following fertilization (conception), the developing human individual is made up of a cell called a zygote; thus, at conception, the first characteristic of life is present. However, this is not all that is necessary to establish life so let’s continue by examining the other characteristics.

Reproduction

The authors describe reproduction by explaining that “all organisms produce new organisms through a process called reproduction.”[1]  There is no small debate in the scientific community on the appropriateness of including reproduction in the list of criteria for living things because there are a number of organisms that are alive that do not reproduce.  One such counterexample is the mule (a crossbred male donkey and female horse). All mules cannot reproduce because their genetic structure does not allow for the creation of viable sperm or egg cells.  Despite their genetic sterility, it is clear to any casual observer or scientist that the mule is alive.

The reason reproduction has remained included in the list of characteristics of living things is that this list is rooted in Darwinian evolutionary theory and reproduction is a necessary process for evolution.  For the biblical worldview, evolution is not a requirement to our understanding of biology which would free us from the need for this characteristic to remain included.  Nevertheless, since we are discussing the scientific perspective on this page, let’s still examine this characteristic with regard to the developing human individual.

Prior to conception, each sperm cell and each egg cell are incapable of reproduction on their own.  Regardless of how long we wait, there is no process by which the individual sperm cell or the individual egg cell will ever be able to produce a new organism on their own.  Once conception occurs, the story changes.  While it is true that first cell (zygote) cannot immediately have a baby, this new cell has everything it needs to eventually have babies.  This cell simply needs to grow and develop to reach the point of maturity (puberty) to be able to have babies.

The strictest interpretation of this characteristic, however, might leave us with a question: If the first cell formed by conception can’t have babies immediately, then does that mean this first cell isn’t alive? The problem is that if we accepted this, then it would imply that the developing human individual isn’t alive until puberty. It would also imply that anyone who is infertile and women after menopause are also not alive. Obviously, these suggestions are absurd. (This is called a proof by contradiction.) The strictest interpretation of this characteristic is false because there are just too many counterexamples. It simply fails to adequately describe life.

In order to overcome these issues, many biologists take the approach of analyzing this characteristic for the species rather than the individual organism. In other words, humans in general can reproduce, so even if a specific individual human cannot reproduce, that individual would still satisfy this characteristic. Since this first cell formed by conception is a human cell (i.e. has human DNA), then this characteristic is also satisfied at conception using this approach.

Genetic Code

In expanding on this characteristic, the textbook explains that “biologists now know that the directions for inheritance are carried by a molecule called deoxyribonucleic acid, or DNA. This genetic code, with a few minor variations, determines the inherited traits of every organism on Earth.”[1] So, at what point does the developing individual human have DNA.

One of the key events that occurs during fertilization is the combination of genetic material from the sperm cell and egg cell.  Prior to conception, both the sperm and the egg cell each have half of the DNA of a normal human cell (the sperm carrying its half from the father and the egg carrying its half from the mother). During fertilization, the half of the DNA from the sperm joins to the half of the DNA from the egg thereby establishing the full genetic code of a normal human cell.

Thus, at fertilization, all of the unique genetic traits of the developing human individual are established.  We know that these genetic traits include gender, hair color, eye color, tendency to be tall, skin tone, etc. Interestingly, there is evidence that these genetic traits even include ability (cognitive and physical) and personality (such as creative or analytical).  So, the individual characteristics of the developing individual human are embedded in their unique genetic code which is established at conception.  But I digress, what’s relevant here is simply that the first cell after conception does have DNA, satisfying this characteristic of life.

Growth and Development

In the discussion of growth and development, the textbook explains that “All living things grow during at least part of their lives. For some single-celled organisms, such as bacteria, growth is mostly a simple increase in size. Multicellular organisms, however, typically go through a process called development. During development, a single fertilized egg cell divides again and again to produce the many cells of mature organisms. As those cells divide, they change in shape and structure to form cells such as liver cells, brain cells, and muscle cells. This process is called differentiation, because it forms cells that look different from one another and perform different functions.”[1] This text clearly illustrates that this characteristic is present immediately following fertilization (conception).  Nevertheless, let’s describe this process of growth and development that begins following conception here.

Prior to conception, the individual sperm cell is not growing or dividing.  Similarly, prior to conception, the individual egg cell (oocyte) is not growing or dividing.  However, once fertilization (conception) occurs, the newly formed cell (zygote) begins to divide – increasing the number of cells.  The first stage of this division that begins immediately after fertilization is called cleavage; in this stage “the relatively enormous zygote directly subdivides into many smaller cells of conventional size.”[2] This division begins in the fallopian tube as the zygote travels to the uterus and continues in the uterus prior to implantation.  By the time implantation occurs, there are several hundred cells that have formed what is termed a “blastocyst” which has a diameter of 0.2mm – twice the size of the first cell (zygote).2  Altogether, this describes a process of growth and development that begins at fertilization and that will continue beyond implantation.  Thus, it is at fertilization (conception) that the characteristic of growth and development begins.

Metabolism (Obtain and Use Materials and Energy)

The textbook explains that “Organisms also need materials and energy just to stay alive. The combination of chemical reactions through which an organism builds up or breaks down materials as it carries out its life processes is called metabolism.”[1] Now that we understand what metabolism is, the relevant question becomes when metabolism begins for the developing human individual.

One of the things that occurs during fertilization is the “activation” of the egg cell’s metabolism – an event termed “Oocyte Activation” by the scientific community.  Many scientists, like the authors of the article “Egg Activation at Fertilization:  Where It All Begins”[3], are still learning what causes the metabolism of the egg to activate during fertilization.  Regardless of the underlying causes, the fact remains that it is at fertilization (conception) that metabolism begin.  So, it is again at fertilization that this characteristic of life is present.

Respond to Their Environment

The authors further explain this characteristic in the textbook by stating that “organisms detect and respond to stimuli from their environment. A stimulus is a signal to which an organism responds.”[1] Now, notice that the definition of a stimulus is very broad. A stimulus is basically anything that causes the organism to respond. So, our question here is whether a zygote (the first cell formed by fertilization) exhibits any such response to stimuli.

To answer this question, we’re going to examine an activator called paf (platelet-activating factor) because it has been so well studied in early embryo development, even for the zygote (the first cell formed by fertilization). Paf is part of a developmental loop for the embryo in that it is first produced and secreted by the embryo and then the embryo responds to its presence to create a virtuous cycle of growth. While the embryo does produce its own paf, it can also be synthesized and introduced independently; either way, paf is known to “stimulate embryo metabolism [i.e. activity], cell cycle progression [i.e. growth], and embryo viability”[4]. The author of this article notes that this response is present even for zygotes (the first cell formed at fertilization): “paf is made by and acts upon the zygote”[4].

Allow me to give a related example that might be a bit more illustrative. In clinical practice, the goal is often to encourage the embryo to produce its own paf (because embryo-produced paf has a more potent effect on development). One way to do this is to introduce a protein (albumin) to the embryo’s environment. This protein serves as a stimulus that the embryo then responds to by producing more paf. This response can be directly observed because when it occurs there is a calcium byproduct (Ca2+) that is produced in the process. To our point here, does a zygote display this measurable response to this stimulus? Indeed, studies have shown that when a zygote is exposed to this protein (albumin), this calcium byproduct (Ca2+) begins to show up, evidencing a response to this stimulus.[4]

I realize some of the specific terms here might not be the easiest to follow. Let me just summarize by saying that the zygote (the first cell formed at conception) does indeed respond to simuli in their environment. One example is that whenever a protein (called albumin) is introduced into the zygote’s environment, they respond by producing a compound (called paf). Furthermore, whenever this compound (paf) is present, even if it’s introduced artificially, the zygote responds to it with growth and activity.

Maintain a Stable Internal Environment

“Even though conditions in the external environment may vary widely, most organisms must keep internal conditions, such as temperature and water content, fairly constant to survive. The process by which they do this is called homeostasis.”[1] As just one example of homeostasis, let’s focus on balancing water content.  Cells that have too much water become bloated and can even burst, whereas cells that have too little shrink and fail to function.

Upon fertilization, the first cell is traveling in the fallopian tubes to the uterus.  In the fallopian tubes, oxygen, water, and nutrients are always available. That first cell must regulate how much to take in and how much to expel to maintain a balance of water. That first cell does not burst from taking too much in and does not shrivel from letting too much out while traveling in the fallopian tube. That simple fact is evidence that the developing human individual maintains homeostasis from the point of fertilization, satisfying this characteristic of life.

Evolution

The last characteristic identified by the authors – “Taken as a group, living things change over time”[1] – describes the theory of evolution of a species.  Of course, the biblical world view does not require that we accept the theory of evolution as true; nevertheless, this characteristic is fairly easy to evaluate.  At the time of fertilization, the first cell is a human cell (i.e. with human DNA). This means that, at the time of fertilization, this cell belongs to the human species, a species that evolves according to evolutionary theory.  So, even from this evolutionary biology lens, the developing human individual satisfies this characteristic at fertilization.

Summary

In summation, all the characteristics of living things are present immediately after fertilization (conception).  Furthermore, they are not all present just before fertilization. As such, according to the biological definition, the developing individual human’s first cell is a living organism. So, we can say that life begins at fertilization (conception).

The experts on studying and defining life, biologists, have all resolved that it is the presence of these things that define something as alive. It’s not the presence of a heartbeat, detectable brainwaves, or anything else that defines life. Life does begin at conception. Now, as mentioned above, this does not resolve the debate regarding whether this living organism is a human person; we discuss that question further in our overview and on our page titled When Is a Person a Person | Scientifically.

[1] Miller, K. R., & Levine, J. S. (2008). Prentice Hall Biology. Upper Saddle River, NJ: Pearson/Prentice Hall.

[2] Sapunary, D., & Arey, L. B. (2017, March 21). Prenatal Development. (Encyclopaedia Britannica, Inc.) Retrieved May 19, 2017, from Encyclopaedia Britannica: https://www.britannica.com/science/prenatal-development

[3] Runft, L. L., Jaffe, L. A., & Mehlmann, L. M. (2002). Egg Activation at Fertilization: Where It All Begins. Developmental Biology(245), 237-254.

[4] Chris O’Neill, The role of paf in embryo physiology, Human Reproduction Update, Volume 11, Issue 3, May/June 2005, Pages 215–228, https://doi.org/10.1093/humupd/dmi003